Hi ROG!
Your last part of the video is slightly frightening though. When I get this copyright claim (had seen one before) it came with the message that it had no consequences for my YouTube channel or video. Are you saying that it also can happen that a copyright claim CAN have consequences? Let's hope that will never happen to you, me or anybody else here on the forum.
First thing is to distinguish between the composer and the copyright holder, who may or not be the same person.
Copyright can also exist separately on a recording of the song, meaning that several copyright holders can be involved.
I speak from practical experience here - one of our strikes had six copyright claims, not of which were upheld.
Once the computer has thrown up a positive, the copyright holder(s) are informed and they can assess the situation
and either withdraw the claim, or continue with it. If they choose to continue, they may allow use of the track but claim
any advertising revenue which the track generates. Alternatively, they may ask for the video to be taken down and you
should do this without delay. Exceptionally, they can move straight to a legal action against you for infringement and this
is the event to which I referred when I said you can lose everything you own. This last option is unlikely, but technically possible.
Hope this makes things clear.
ROG.